3,4-Dihydroxy-3-cyclobutene-1,2-dione (usual name: "squaric acid") is known as a useful starting material for pharmaceuticals, in addition to functional materials such as photosensitive materials for electrophotography, medium material for optical discs, optical sensitizers, and the like [Chemical Reviews, 93, 449, (1993); Japanese Patent Application, First Publication Laid Open No. Hei 4-106400; Japanese Patent Application, First Publication Laid Open No. Hei 2-306247; Japanese Patent Application, First Publication Laid Open No. Hei 2-48665; Japanese Patent Application, First Publication Laid Open No. Hei 5-5005; Japanese Patent Application, First Publication Laid Open No. Hei 5-96173; and the like].
Hitherto, several methods for manufacturing 3,4-dihydroxy-3-cyclobutene-1,2-dione are known. However, all known methods have problems such as need for many steps, difficulty in synthesizing starting materials, hard reaction conditions, low yields, requirements for special manufacturing equipment, and the like.
Examples of the known methods include (1) a method using a triketene as a starting material (disclosed in Jackson, B. et. al., EP442431, and the like); (2) a method using 4-hydroxy-3-cyclobutene-1,2-dione as a starting material [disclosed in Bellus, D. et. al., Helv. Chim. Acta, 61, 1784 (1978)]; (3) a method using a tetraalkoxyethylene as a starting material [disclosed in Bellus, D., J. Org. Chem., 44, 1208 (1979)]; (4) a method using a dialkoxyacetylcne as a starting material [disclosed in Pericas, M. A., Tetrahedron Letters, 4437 (1977)]; (5) a method using a tetrahalogenoethylene as a starting material [disclosed in J. Amer. Chem. Soc., 81, 3480 (1959), and the like]; (6) a method using hexachlorobutadiene as a starting material (disclosed in Hagenberg, P. et. al., Ger. Offen, No. 1568291, and the like); (7) a method using carbon monoxide as a starting material [disclosed in Silvestri, G. et. al., Electrochim. Acta, 23, 413 (1978)]; and the like.
However, each of the aforementioned methods has the following problems. That is, according to the method (1), it is difficult to obtain a large amount of the starting material since a triketene is a side product in the production of a diketene. According to the method (2), the method for acquiring the starting material is a solid culturing method with poor productivity or a synthetic method requiring many steps. The method (3) has a difficulty in synthesizing the starting materials, in addition to a low yield. The method (4) has a difficulty in synthesizing the starting materials. The method (5) has a difficulty in synthesizing the starting materials, in addition to requiring many steps. The method (6) provides a low yield. The method (7) requires special manufacturing equipment.
Further, in Liebigs Ann. Chem., 686, 55 (1965), a method for manufacturing 3,4-dihydroxy-3-cyclobutene-1,2-dione from 1,1,2,3,4,4-hexachloro- 1,3-butadiene is disclosed. However, this method provides a low yield of the desired final product.
In addition, in J. Amer. Chem. Soc., 84, 2919 (1962), a method for manufacturing 3,4-dihydroxy-3-cyclobutene- 1,2-dione via 2-chloro-3-ethoxy-4,4-difluolo-2-cyclobutene-1-one is disclosed. However, this method has problems such as a low yield in the synthesis of the starting material, 1-chloro-2,4,4-triethoxy-3,3-difluolocyclobutene, and a low yield of the desired final product.
Additionally, a method for manufacturing a 3-alkoxy-2-halogcnocyclobutanone derivative, which is used as an intermediate in producing 3,4-dihydroxy-3-cyclobutcne-1,2-dione in the present invention, is disclosed in Abramova, N. M. et. al., Izv. Akad. Nauk SSSR, Scr. Khim., 2, 439 (1981). However, the yield of the desired product according to this method is as low as 35%, which is unsatisfactory for a practical use.
The object of the present invention is to provide a method for manufacturing 3,4-dihydroxy-3-cyclobutcne-1,2-dione, easily and efficiently.